International organisations grew out of the diplomatic conferences of the nineteenth century as states sought more effective ways to deal with problems caused by the rapid development of international society. The International Telegraphic (later Telecommunications) Union and the Universal Postal Union were founded in the 1860s. There are now countless international organisations, ranging from large ones with global responsibilities and virtually universal membership, such as the United Nations and the UN specialised agencies, to regional or highly specialised organisations, such as the (large) European Union and the (tiny) International Whaling Commission. Although each organisation is different and must be studied separately, they share the following basic characteristics:

• Establishment by treaty (constituent treaty), although there are some exceptions. The Organization for (previously Conference on) Security and Co-operation in Europe (OSCE/CSCE), emerged following the Helsinki Final Act 1975, which was not a treaty. Nor was the Commonwealth or its secretariat established by treaty. The International Committee of the Red Cross (ICRC) is a Swiss corporation, and states are not members of it. However, it has a special place internationally, being regarded with particular respect by governments and referred to in (and sometimes a party to) treaties.

• Membership limited exclusively or primarily to states. This is reflected in the alternative generic term ‘intergovernmental organisation’. […]